bison/src/closure.c

/* Closures for Bison

   Copyright (C) 1984, 1989, 2000, 2001, 2002, 2004, 2005, 2007 Free
   Software Foundation, Inc.

   This file is part of Bison, the GNU Compiler Compiler.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>
#include "system.h"

#include <bitset.h>
#include <bitsetv-print.h>
#include <bitsetv.h>
#include <quotearg.h>

#include "closure.h"
#include "derives.h"
#include "getargs.h"
#include "gram.h"
#include "reader.h"
#include "symtab.h"

/* NITEMSET is the size of the array ITEMSET.  */
item_number *itemset;
size_t nitemset;

static bitset ruleset;

/* internal data.  See comments before set_fderives and set_firsts.  */
static bitsetv fderives = NULL;
static bitsetv firsts = NULL;

/* Retrieve the FDERIVES/FIRSTS sets of the nonterminals numbered Var.  */
#define FDERIVES(Var)   fderives[(Var) - ntokens]
#define   FIRSTS(Var)   firsts[(Var) - ntokens]


/*-----------------.
| Debugging code.  |
`-----------------*/

static void
print_closure (char const *title, item_number *array, size_t size)
{
  size_t i;
  fprintf (stderr, "Closure: %s\n", title);
  for (i = 0; i < size; ++i)
    {
      item_number *rp;
      fprintf (stderr, "  %2d: .", array[i]);
      for (rp = &ritem[array[i]]; *rp >= 0; ++rp)
	fprintf (stderr, " %s", symbols[*rp]->tag);
      fprintf (stderr, "  (rule %d)\n", -*rp - 1);
    }
  fputs ("\n\n", stderr);
}


static void
print_firsts (void)
{
  symbol_number i, j;

  fprintf (stderr, "FIRSTS\n");
  for (i = ntokens; i < nsyms; i++)
    {
      bitset_iterator iter;
      fprintf (stderr, "\t%s firsts\n", symbols[i]->tag);
      BITSET_FOR_EACH (iter, FIRSTS (i), j, 0)
	{
	  fprintf (stderr, "\t\t%s\n",
		   symbols[j + ntokens]->tag);
	}
    }
  fprintf (stderr, "\n\n");
}


static void
print_fderives (void)
{
  int i;
  rule_number r;

  fprintf (stderr, "FDERIVES\n");
  for (i = ntokens; i < nsyms; i++)
    {
      bitset_iterator iter;
      fprintf (stderr, "\t%s derives\n", symbols[i]->tag);
      BITSET_FOR_EACH (iter, FDERIVES (i), r, 0)
	{
	  fprintf (stderr, "\t\t%3d ", r);
	  rule_rhs_print (&rules[r], stderr);
	}
    }
  fprintf (stderr, "\n\n");
}

/*------------------------------------------------------------------.
| Set FIRSTS to be an NVARS array of NVARS bitsets indicating which |
| items can represent the beginning of the input corresponding to   |
| which other items.                                                |
|                                                                   |
| For example, if some rule expands symbol 5 into the sequence of   |
| symbols 8 3 20, the symbol 8 can be the beginning of the data for |
| symbol 5, so the bit [8 - ntokens] in first[5 - ntokens] (= FIRST |
| (5)) is set.                                                      |
`------------------------------------------------------------------*/

static void
set_firsts (void)
{
  symbol_number i, j;

  firsts = bitsetv_create (nvars, nvars, BITSET_FIXED);

  for (i = ntokens; i < nsyms; i++)
    for (j = 0; derives[i - ntokens][j]; ++j)
      {
	item_number sym = derives[i - ntokens][j]->rhs[0];
	if (ISVAR (sym))
	  bitset_set (FIRSTS (i), sym - ntokens);
      }

  if (trace_flag & trace_sets)
    bitsetv_matrix_dump (stderr, "RTC: Firsts Input", firsts);
  bitsetv_reflexive_transitive_closure (firsts);
  if (trace_flag & trace_sets)
    bitsetv_matrix_dump (stderr, "RTC: Firsts Output", firsts);

  if (trace_flag & trace_sets)
    print_firsts ();
}

/*-------------------------------------------------------------------.
| Set FDERIVES to an NVARS by NRULES matrix of bits indicating which |
| rules can help derive the beginning of the data for each           |
| nonterminal.                                                       |
|                                                                    |
| For example, if symbol 5 can be derived as the sequence of symbols |
| 8 3 20, and one of the rules for deriving symbol 8 is rule 4, then |
| the [5 - NTOKENS, 4] bit in FDERIVES is set.                       |
`-------------------------------------------------------------------*/

static void
set_fderives (void)
{
  symbol_number i, j;
  rule_number k;

  fderives = bitsetv_create (nvars, nrules, BITSET_FIXED);

  set_firsts ();

  for (i = ntokens; i < nsyms; ++i)
    for (j = ntokens; j < nsyms; ++j)
      if (bitset_test (FIRSTS (i), j - ntokens))
	for (k = 0; derives[j - ntokens][k]; ++k)
	  bitset_set (FDERIVES (i), derives[j - ntokens][k]->number);

  if (trace_flag & trace_sets)
    print_fderives ();

  bitsetv_free (firsts);
}



void
new_closure (unsigned int n)
{
  itemset = xnmalloc (n, sizeof *itemset);

  ruleset = bitset_create (nrules, BITSET_FIXED);

  set_fderives ();
}



void
closure (item_number *core, size_t n)
{
  /* Index over CORE. */
  size_t c;

  /* A bit index over RULESET. */
  rule_number ruleno;

  bitset_iterator iter;

  if (trace_flag & trace_sets)
    print_closure ("input", core, n);

  bitset_zero (ruleset);

  for (c = 0; c < n; ++c)
    if (ISVAR (ritem[core[c]]))
      bitset_or (ruleset, ruleset, FDERIVES (ritem[core[c]]));

  /* core is sorted on item index in ritem, which is sorted on rule number.
     Compute itemset with the same sort.  */
  nitemset = 0;
  c = 0;
  BITSET_FOR_EACH (iter, ruleset, ruleno, 0)
    {
      item_number itemno = rules[ruleno].rhs - ritem;
      while (c < n && core[c] < itemno)
	{
	  itemset[nitemset] = core[c];
	  nitemset++;
	  c++;
	}
      itemset[nitemset] = itemno;
      nitemset++;
    };

  while (c < n)
    {
      itemset[nitemset] = core[c];
      nitemset++;
      c++;
    }

  if (trace_flag & trace_sets)
    print_closure ("output", itemset, nitemset);
}


void
free_closure (void)
{
  free (itemset);
  bitset_free (ruleset);
  bitsetv_free (fderives);
}